1. Field of the Invention
The present invention relates generally to a gasket for sealing a refrigerant compressor and, more particularly, to a metallic gasket covered with an elastic coating and adapted for providing a connecting portion, between a cylinder block and an end housing of a refrigerant compressor, and between high and low pressure regions inside the compressor, with a stable fluid-tight sealing.
2. Description of the Related Art
In conventional refrigerant compressors such as swash plate type refrigerant compressors, a pair of front and rear cylinder blocks are axially combined together to define, inside a joint region of the cylinder blocks, a swash plate chamber in which a refrigerant returning from an external refrigerating system is introduced to be compressed. The opposite ends of the combined front and rear cylinder blocks, located away from each other, are closed by front and rear housings via front and rear valve assemblies.
Each of the front and rear housings is provided with a radially outer suction chamber for the refrigerant gas before compression and a radially inner discharge chamber for the compressed refrigerant gas. The combined front and rear cylinder blocks are provided with a common central shaft bore for receiving therein an axial drive shaft. A swash plate is fixedly mounted on the drive shaft so as to rotate together with the drive shaft within the swash plate chamber. The combined front and rear cylinder blocks are also provided with a plurality of axially extending cylinder bores in which double headed pistons, operatively engaged with the swash plate via shoes, are received. The double headed pistons are reciprocated by the rotating swash plate in the cylinder bores to implement suction and compression of the refrigerant gas, and to discharge the compressed refrigerant gas.
The front and rear valve assemblies include front and rear valve plates, respectively, and a discharge valve member and a suction valve member are combined with each of the front and rear valve plates. Each of the valve plates is provided with plural suction ports bored therein and fluidly connected to the associated suction chamber. The suction ports of each valve plate are openably closed by the suction valve member. Each of the valve plates is also provided with plural discharge ports bored therein and fluidly connected to the associated discharge chamber. The discharge ports of each valve plate are openably closed by the discharge valve member.
The discharge ports of the front and rear valve plates are arranged to be in registration with the cylinder bores of the front and rear cylinder blocks to discharge the compressed refrigerant gas from the cylinder bores toward the front and rear discharge chambers through the discharge valve members. The front and rear suction chambers and the swash plate chamber fluidly communicate by suction passageways formed in the combined cylinder blocks. Similarly, the front and rear discharge chambers fluidly communicate by discharge passageways formed in the combined cylinder blocks.
The outer framework of the refrigerant compressor provided by the above-mentioned combined front and rear cylinder blocks and the front and rear housings must be completely sealed against the atmospheric environment therearound. Further, since the compressor has, in the interior thereof, a low pressure region in which a suction pressure prevails, and a high pressure region in which a high pressure substantially corresponding to the compressed gas pressure prevails, the high and low pressure regions within the compressor must also be appropriately isolated from each other. Thus, gaskets have been suitably incorporated in the compressor and interposed between the respective valve assemblies and housings.
One of the typical gaskets assembled in a generally cylindrical body of a conventional refrigerant compressor is made of a metallic base plate coated with a thin elastic membrane. The typical gasket also includes an outer sealing portion in the shape of a circular rim, and an inner sealing portion in the shape of an annular rim arranged inside the outer sealing portion. The longitudinal ends of the annular, inner sealing portion are curved to extend toward the outer sealing portion and are connected to the latter. The outer sealing portion functions to seal a circumferential region of the outer framework of the compressor against the atmosphere, and the inner sealing portion functions to seal a boundary between the high and low pressure regions within the compressor.
In such a conventional gasket, each of the inner and outer sealing portions is generally provided with an elastically deformable central ridge for a sealing function. FIG. 5 shows the cross-sectional shape of one sealing portion, having a width W.sub.1, of the conventional gasket. As shown in FIG. 5 the sealing portion 51 is provided with a central ridge 52 having a width W.sub.2, occasionally referred to as "a bead", and a pair of flat side parts 53, 54 integrally joined to the central ridge 52, respectively having widths W.sub.3 and W.sub.4. The central ridge 52 is formed as a smoothly curved projection projecting from the flat side parts 53, 54 and having an apex 52a continuously running along the entire length of the sealing portion 51. The flat side parts 53, 54 also extend along the entire length of the sealing portion 51 to define the peripheral edge of the gasket.
When the sealing portion 51 of the gasket is compressed between two structural members to be sealed, such as the valve plate and the housing of the compressor, the apex 52a of the central ridge 52 is closely abutted to one structural member and the surfaces, away from the apex 52a, of the flat side parts 53, 54 are closely abutted to another structural member, and thereby a fluid-tight or hermetical sealing is established between the members. At this time, only the central ridge 52 having the width W.sub.2, which is the difference between the entire width W.sub.1 of the sealing portion 51 and the widths W.sub.3, W.sub.4 of the side parts 53, 54, is elastically deformed and collapsed under compression to enhance the fluid-tight sealing. That is, the sealing portion 51 is capable of being elastically deformed in only a part "W.sub.2 " thereof.
It is also known in the art that the gasket with the above-mentioned structure is further provided with plural valve retainers formed integrally with the gaskets, as disclosed in, e.g., Japanese Unexamined Utility Model Publication (Kokai) No. 4-125682. In this gasket, the valve retainers are located, in connection with the respective discharge ports of the valve plate, in the compressor adjacent to the discharge valve member for determining an amount of opening of the discharge valve member.
The gasket including integral valve retainers generally requires a thickness of a metallic base plate of the gasket, sufficient to ensure the mechanical strength of the retainers. Thus, this type of gasket in practical use is made of a metallic base plate having a thickness in the order of 0.6 mm to 1.0 mm, which is generally considered a thicker material used for a soft metallic gasket.
If the gasket made of a metallic base plate having a thickness not less than 0.6 mm includes the sealing portion 51 which includes the central ridge 52 formed partially in width of the sealing portion, significant strength is provided to the central ridge 52 because the width W.sub.2 thereof is a little larger than the height h.sub.1 between the apex 52a and the bottom faces of the side parts 53, 54 (see FIG. 5). As a result, the gasket has a defect in that it is difficult to elastically deform or collapse the central ridge 52, under compression between two structural members to be sealed, to a degree sufficient to establish an effective, stable fluid-tight sealing.